Subunit interactions and conformational changes are important to the activity and regulation of many enzymes, particularly allosteric ones. We are investigating the protein-protein interactions of aldolase, hexokinase, and lactate dehydrogenase in an attempt to determine what kinds of interactions are important to enzyme activity and regulation. We are looking to see how modification of aldolase by enzymatic hydrolysis or with derivatizing reagents will alter the dissociation and conformational properties from those of the native enzyme. Hexokinase has been found to dimerize at a lower enzyme concentration in the presence of substrates, indicating that the substrates are producing a conformational change which facilitates dimerization. Preliminary experiments indicate that human red blood cell hexokinase may be regulated by D-2,3-diphosphoglycerate. Lactate dehydrogenase is being modified in order to see if the dissociation in 1.2 M MgCl2 is affected. There will be further investigation into the possibility that LDH dissociates at elevated temperatures.